@Ankit: "how all programmable devices consume less power?"
This is a complicated question. An ASIC/SoC uses the least power and gives the best performance, but it costs millions of dollars and takes at least a year (maybe two) to design and build. An FPGA consumes more power and offers less performance than an ASIC/SoC, but you can implement a design much faster and cheaper.
A microprocessor/microcontroller is really cheap, and great at implementing decision-making software, but it' svery ineffuicient at performing algorithmic data processing tasks. An FPGA can perform algorithmic dataprocessing tasks at a lower clock rate using less power because it can do things in a massivelt parallel fashion